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We thank Barroso et al for providing a summary of their pilot study to evaluate methods and barriers to recruitment of commercial sex workers (CSWs) in Rio de Janeiro, Brazil. As they note, HIV efficacy trials require enrollment of large and diverse cohorts of participants that reflect the demographics of high-risk individuals. This may ensure that summary measures of efficacy are most applicable to populations in greatest need of HIV vaccines.1 Because vaccine effects could differ between female and male populations, as has been suggested from herpes vaccine trials,2,3 and because interpretation of surrogate endpoints (eg, viral load set point) may be influenced by gender,4,5 HIV vaccines should be evaluated in both populations, when possible.

In their study, Barroso et al report that despite extensive outreach, only 7.8% of CSWs visited the vaccine trial site and less than 1% actually enrolled in the Phase IIB trial. Several of the social and cultural barriers that they enumerate (eg, lack of understanding of rationale for vaccine trials, transportation, clinic hours, and lack of reliable contact information) are barriers that can be addressed through ongoing work within high-risk communities and innovative logistical solutions (eg, extended clinic hours, providing cell phone time and/or voicemail boxes, and use of community outreach workers). Such strategies often require long-standing relationships with communities at risk, ongoing community education, and sufficient resources to staff outreach and flexible clinic hours. When these strategies are implemented, female CSW populations can be successfully recruited and retained, as noted in our vaccine feasibility study6 and in the subsequent Phase IIB vaccine trial.7

However, one of the most important challenges remaining is to recruit female populations with high HIV incidence in the United States. One reason for low HIV incidence rates in these trials is likely due to the fact that all participants receive extensive risk reduction counseling and linkage to local prevention services, with resultant substantial declines in HIV risk.6,8 Another reason may be low HIV prevalence in male partners. In Brazil, for example, where a simultaneous focus on ensuring access to prevention and treatment services has helped keep the epidemic stable, national adult HIV prevalence has remained stable at 0.5% since 2000.9 In fact, a limited number of studies on HIV seroincidence estimates among CSWs in South America have acknowledged rates as low as 0%.10-13

Efforts are currently underway to develop and test novel strategies to recruit high-incidence cohorts of women into trials through 2 National Institutes of Health-funded clinical trials networks: the HIV Vaccine Trials Network and the HIV Prevention Trials Network. These efforts build upon the efforts of investigators like our Brazilian colleagues, and investigators in the previously reported HIV Vaccine Trials Network 903 study, to ensure that future HIV vaccine trials are able to fully evaluate vaccine effects in women.